For control of electro-injectors it is known to supply each of them with a current, whose time plot comprises a rise portion increasing up to a first hold value, an amplitude oscillating portion about the first hold value, a fall portion decreasing down to a second hold value, an amplitude oscillating portion about the second hold value, and a fall portion down to an approximately zero value.
For control of electrovalves, for example electrovalves for controlling intake and exhaust valves, it is known to supply each of them with a current, whose time plot comprises a rise portion increasing up to a first hold value, an amplitude oscillating portion about the first hold value, a rise portion increasing up to a second hold value, an amplitude oscillating portion about the second hold value, a fall portion decreasing down to a third hold value, an amplitude oscillating portion about the third hold value, and finally a fall portion decreasing down to an approximately zero value.
Driving of the electrovalves is obtained via a control device comprising, for each electrovalve, a pair of controlled switches, which are arranged in series to the electrovalve, one of which connects the electrovalve to a supply line and the other connects the electrovalve to a ground line; and a free-wheeling diode connected between one of the terminals of the electrovalve and the ground line.
During the decrease of the current from the third hold value to a substantially zero value, both of the controlled switches are simultaneously open and the current circulating in the electrovalve is discharged towards the ground line, through the free-wheeling diode and the controlled switch connected to the ground line. The latter operates in the breakdown region, and dissipated thereon by the avalanche effect is the energy stored in the electrovalve, which is equal to:
  E  =            1      2        ·          L      ev        ·          I      ev_h      2      where Iev—h is the initial value of the current circulating in the electrovalve, equal to the value reached in the previous step, and Lev is the equivalent inductance of the electrovalve.
By substituting typical numerical values, it is possible to verify immediately that the energy dissipated on the controlled switch is equal to approximately 10 mJ, a value such as to cause a considerable overheating of the controlled switch.
Given that the controlled switches are normally MOSFET transistors, it is thus necessary to use transistors having packages of sufficiently large dimensions as to be able to dissipate the high energy values involved.
Considering a four-cylinder engine, of which at least the two intake valves of each cylinder are controlled, and operating at 3500 r.p.m. with a dual actuation of the electrovalves for each engine rev, a dissipation of power equal to approximately 4.7 W is obtained on the basis of the previously calculated value, only due to the avalanche effect in the controlled switches. To said value the power dissipated by conduction during actuation of the electrovalves is then to be summed.
Driving of the electro-injectors is obtained via a control device having a circuit architecture similar to the one used for driving the electrovalves, so that the integration in the same engine control unit of both of the devices for controlling the electrovalves and the electro-injectors leads to considerable problems linked principally to the dissipation of the high powers involved and to the integration in reduced dimensions of all the electronic components.
Currently, the problems linked to the high dissipation of power in the engine control unit are overcome by resorting to costly technologies, which envisage, among other things, the use of ceramic substrates or hybrid circuits.
The purpose of the present invention is thus to provide a single device for controlling electro-injectors and electrovalves that will enable the above drawbacks to be overcome.
According to the present invention, a single device for controlling electro-injectors and electrovalves, and a method of operating the same are consequently provided, as defined in claims 1 and 11, respectively.